On Wed, Jul 24, 2024 at 12:49 PM Andrew Morton
<akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Tue, 9 Jul 2024 16:30:53 +0000 Frank van der Linden <fvdl@xxxxxxxxxx> wrote:
>
> > In addition to the number of allocations and releases, system
> > management software may like to be aware of the size of CMA
> > areas, and how many pages are available in it. This information
> > is currently not available, so export it in total_page and
> > available_pages, respectively.
> >
> > The name 'available_pages' was picked over 'free_pages' because
> > 'free' implies that the pages are unused. But they might not
> > be, they just haven't been used by cma_alloc
> >
> > The number of available pages is tracked regardless of
> > CONFIG_CMA_SYSFS, allowing for a few minor shortcuts in
> > the code, avoiding bitmap operations.
> >
> > ...
> >
> > @@ -382,7 +383,7 @@ static void cma_debug_show_areas(struct cma *cma)
> > {
> > unsigned long next_zero_bit, next_set_bit, nr_zero;
> > unsigned long start = 0;
> > - unsigned long nr_part, nr_total = 0;
> > + unsigned long nr_part;
> > unsigned long nbits = cma_bitmap_maxno(cma);
> >
> > spin_lock_irq(&cma->lock);
> > @@ -394,12 +395,12 @@ static void cma_debug_show_areas(struct cma *cma)
> > next_set_bit = find_next_bit(cma->bitmap, nbits, next_zero_bit);
> > nr_zero = next_set_bit - next_zero_bit;
> > nr_part = nr_zero << cma->order_per_bit;
> > - pr_cont("%s%lu@%lu", nr_total ? "+" : "", nr_part,
> > + pr_cont("%s%lu@%lu", start ? "+" : "", nr_part,
> > next_zero_bit);
> > - nr_total += nr_part;
> > start = next_zero_bit + nr_zero;
> > }
>
> Can you please explain the above change?
Sure - there's no need anymore to keep a count of available pages for
the debug output, since that's already tracked in the available_count
field. So, 'nr_total' can be removed. But you still need to check for
this being the first instance of the loop, so use 'start' for that
instead.
>
> > - pr_cont("=> %lu free of %lu total pages\n", nr_total, cma->count);
> > + pr_cont("=> %lu free of %lu total pages\n", cma->available_count,
> > + cma->count);
> > spin_unlock_irq(&cma->lock);
> > }
> >
> > @@ -446,6 +447,10 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> >
> > for (;;) {
> > spin_lock_irq(&cma->lock);
> > + if (count > cma->available_count) {
>
> Right here would be a nice place for a comment?
>
Yes, I'll add one.
> > + spin_unlock_irq(&cma->lock);
> > + break;
> > + }
> > bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
> > bitmap_maxno, start, bitmap_count, mask,
> > offset);
>
I'll re-send a v2 with some Cc: lines added.
Thanks!
- Frank
